1. Field of the Invention
This invention relates to an achromatized beam splitter of low polarization.
2. Description of the Prior Art
A beam splitter provided by forming reflecting film layers on the inclined surfaces of two right isosceles triangular prisms and joining the inclined surfaces together is known. For example, as shown in FIG. 1 of the accompanying drawings, such a beam splitter may be provided by forming a reflecting layer 13 consisting of a thin film of metal or dielectric material on the inclined surface of a right isosceles triangular prism 11, and joining a right isosceles triangular prism 12 thereto by the use of an adhesive agent. This reflecting layer 13, if it consists of a dielectric multilayer film, eliminates absorption, but the film construction thereof is complex and difficult to manufacture. Also, if this reflecting layer is comprised of a silver monolayer film, the light transmitted therethrough becomes blue and the light reflected thereby becomes yellowish, thus making the so-called achromatization impossible. Further, if the reflecting layer is comprised of a monolayer film of chromium, the loss of quantity of light will be large. The reflecting layer, if it consists of a multilayer film of dielectric material or a monolayer film of metal, results in a large difference in the polarized component between the transmitted light and the reflected light. The amount of such a difference in the polarized component leads to a great problem in some cases. For a construction of a beam splitter which suffers little from polarization, there is known U.S. Pat. 3,559,090. This beam splitter adopts, as the construction of the reflecting layer 13, a construction in which a layer of metal, such as silver, is sandwiched between dielectric layers of a single component having different optical thicknesses.